PYTHIUM 493 



epidermis ; and this is by far the more common ; 

 or 



&. By passage of the hypha through the pore of a 

 stoma : this is the less common mode. 



4. Trace the further course of the hypha through 

 the transparent tissues of the host-plant, noting the 

 rarity, or complete absence of septa. 



IV. From diseased specimens hardened in alcohol, 

 cut transverse sections : mount in weak glycerine, to- 

 gether with a drop of iodine solution, and examine 

 under a high power. In these specimens the above 

 observations are to be severally confirmed : it is 

 further to be noted that the hyphal filaments traverse 

 the cell- walls of the host, showing a slight constric- 

 tion at the point of perforation : also that they traverse 

 the whole epidermis and cortex, either passing directly 

 through the cells, or running along the intercellular 

 spaces. 



V. Place an infected seedling in fresh water, in a flat 

 watch-glass, and examine it at intervals for a day or 

 two under a low power. Many of the filaments will be 

 seen to form swellings at certain points, which assume 

 a spherical form, are filled with granular protoplasm, 

 and are divided off by a septum from the parent 

 filament, while the thin outer wall assumes a darker 

 colour : these swollen bodies are the asexual repro- 

 ductive organs, or resting conidia. Two types are to 

 be distinguished 



1. Terminal conidia, at the ends of the filaments. 



2. Interstitial conidia, which may appear at any 

 other point on the filament. 



It is characteristic of this species that the hypha 



